Selective control of the Rashba spin–orbit coupling in multiple quantum wells.

Resorting to an external gate potential, we explore the spin–orbit coupling (SOC) in n-quantum-well structures with n subbands occupied, since n-well configuration is favorable to the flexible control of n-subband occupation for electrons in experiments. The charge transfer among the multiple local wells provides more possibilities of manipulation of the Rashba SOC. For all the systems we construct, from triple- to septuple-quantum-well structures, the SOC coefficient of the lowest subband is always much larger than those of the other subbands, which leads to greater spin splitting, conducive to desirable spin polarization. Furthermore, we demonstrate selective control of SOC via adjusting the gate, i.e., separately tuning the SOC coefficients of certain subbands while leaving those of the others unaffected by the gate. However, when more local wells are incorporated, the SOC coefficients of all subbands become weak gate-dependent in the case of n-subband occupation. All these findings are attributed to the charge redistribution among the subwells and the variation gradient of the potential energy along the growth direction of the quantum wells. Our results should provide new insight for experimental manipulation of the Rashba SOC in multiple-well structures. • Selective control of Rashba SOC of different subbands is realized in a wide gate potential range , facilitating the realization of persistent spin helix in quantum well semiconductors, which is crucial for spin-coherent transport. • Large spin splitting of the lowest subband is demonstrated, constructive to desirable spin polarization and detection. • When more local wells are incorporated, in the gate range where n subbands are kept occupied , Rashba SOC of all subbands become less gate-dependent. [ABSTRACT FROM AUTHOR]